The present invention relates to an image forming apparatus.
Conventionally, image forming apparatuses have been known as printers and copiers. Especially, attention has been paid to color image forming apparatuses to form full-color images. For example, in a color image forming apparatus, a plurality of image forming sections each corresponding to a different color are arranged in tandem and units thereof are configured opposed to an intermediate transfer section such as an intermediate transfer belt. In such a color image forming apparatus, due to changes in the operation ambience including temperature and humidity and degradation with age of members, the positions of images formed by individual image forming sections are misaligned in some cases. Therefore, a method to correct the image position of each color, which is so-called registration correction processing, is known. For example, Unexamined Japanese Patent Application Publication No. 2005-292760 discloses a method in which the conveyance interval between sheets is increased compared with a predetermined interval, a plurality of correction pattern images are formed in the enlarged region on a conveyance device or an intermediate transfer section, and then the pattern images having been formed in the region between sheets are detected to correct the misalignment of each image position.
Further, with regard to such a type of image forming apparatus, there is known an apparatus provided with a configuration in which a secondary transfer section to transfer an image having been transferred to an intermediate transfer section onto a sheet can be pressed against the intermediate transfer section and separated therefrom.
Incidentally, in the case where the secondary transfer section has been separated from the intermediate transfer section, the intermediate transfer belt is considered to cause deflection. When with this situation, registration correction processing is carried out and then the intermediate transfer belt is rotated, the intermediate transfer belt meanders from side to side (in the main scanning direction), and thereby it becomes possible that the misalignment of the image position with respect to the main scanning direction contains unnecessary fluctuation components. Thereby, it is conceivable that the correction accuracy of the image position with respect to the main scanning direction deceases.
In contrast, in the case where registration correction processing is carried out in the state where the secondary transfer section has been pressed, the problem as described above is inhibited, but it is possible that through the pressure portion between the intermediate transfer section and the secondary transfer section, a pattern image for correction is transferred onto the secondary transfer section. In this case, when a usual print job is executed, an image having been transferred to the secondary transfer section is transferred onto a sheet, resulting in the possibility of print quality degradation. Incidentally, some secondary transfer sections have a cleaning member such as a blade. However, to expect elimination performance to the extent that the above problem is solved from the member, the cost is increased and the mechanism is complicated, which is hardly a response with a good balance.